Geophysical Measurements to Determine the Hydrologic Partitioning of Snowmelt on a Snow‐Dominated Subalpine Hillslope

Abstract

In subalpine watersheds of the intermountain western United States, snowpack melt is the dominant water input to the hydrologic system. The primary focus of this work is to understand the partitioning of water from the snowpack during the snowmelt period and through the remainder of the growing season. We conducted a time‐lapse electrical resistivity tomography (ERT) study in conjunction with a water budget analysis to track water from the snow‐on through snow‐off season (May–August 2015). Seismic velocities provided an estimate of regolith thickness while transpiration measurements from sap flow in conifer trees provided insight into root water uptake. We observed four hydrologic process‐periods and found that deep flow and tree water fluxes are the primary pathways through which water moves off of the hillslope. Overland flow and interflow were negligible. We observed temporal changes in vadose zone water content more than 3.0 m below the surface. Our results show that vertical flow through the thin soil mantle overlaying coarse colluvial regolith was the primary pathway to a local unconfined aquifer.

Uniform and lateral preferential flows under flood irrigation at field scale

“…Previous studies demonstrated that when only one state variable (water content in this study) is changing, interpretations of relative changes from time‐lapse resistivity observations are less impacted by uncertainty in the relationship between inverted resistivity and water contents (Cassiani et al, ; Thayer et al, ). The borehole NMR data in this study provide quantitative details about the volumetric changes of water in the subsurface but at a much smaller scale.…”

“…To compare results from both methods with each other, sections of the resistivity profile around Wells 1 and 2 were directly compared with borehole NMR measurements in these wells just before irrigation and just after flooding has ceased (Figure ). The resistivity values were converted to volumetric water content values based on an Archie's type relationship (Archie, ) from lab measurements that is used to convert from resistivity to water content (Moreno et al, ; Thayer et al, ). The conductivity of the water used in the lab was 381 μS/cm, which was similar to the 389‐μS/cm conductivity of the irrigation water.…”

“…It is an attractive method for the study of transport properties and processes as it provides nearly spatially continuous imaging of the subsurface overcoming some of the drawbacks of more classic hydrologic methods (e.g., Binley & Kemna, 2005;Singha et al, 2015). Previous studies have used ERT successfully to both qualitatively identify hydrologic processes (Moreno, Arnon-Zur, & Furman, 2015) and quantitatively describe changes in hydrologic state variables such as water content (Thayer et al, 2018). In this study, time-lapse ERT is mainly employed to identify wetting front advancement and its characteristics as described in more detail below.…”

“…However, the duration of the application of irrigation water and the hydrologic status of the subsurface at the start of the experiments differed. Archie's type relationship (Archie, 1942) from lab measurements that is used to convert from resistivity to water content (Moreno et al, 2015;Thayer et al, 2018). The conductivity of the water used in the lab was 381 μS/cm, which was similar to the 389-μS/cm conductivity of the irrigation water.…”

Characterizing hydrological processes in a semiarid rangeland watershed: A hydrogeophysical approach

“…Electrical resistivity tomography (ERT), which measures the spatial distribution of subsurface resistivity, has emerged as a useful geophysical tool for studying the subsurface and tracking hydrologic processes. Due to the general tendency of decreasing resistivity with increasing water content, ERT has commonly been used in a time-lapse capacity to monitor infiltration processes at the event scale (Batlle-Aguilar et al, 2009;Dietrich, Weinzettel, & Varni, 2014;Michot et al, 2003) and seasonal moisture fluctuations (French & Binley, 2004;Jayawickreme, Van Dam, & Hyndman, 2008;Kotikian, Parsekian, Paige, & Carey, 2018;Schwartz, Schreiber, & Yan, 2008;Thayer et al, 2018). Other geophysical tools such as seismic refraction and ground-penetrating radar (GPR) can provide valuable information regarding subsurface structure (Holbrook et al, 2014;McClymont, Hayashi, Bentley, & Liard, 2012;Mills, 1990;Neal, 2004;Parsekian, Singha, Minsley, Holbrook, & Slater, 2015).…”